This invention relates to exhaust gas recirculation valves for internal combustion engines and more particularly to solenoid actuated pintle type valves having sequential dual flow stages.
It is known in the art to provide an automotive internal combustion engine with an exhaust gas recirculation (EGR) valve to control a flow of exhaust gases into the engine induction system and limit the formation of nitrogen oxides (NOx) in the engine. Known valve constructions include pintle type valves which have an axially movable valve with a shaped mushroom-like head connected with an axial pintle shaft. The head is seatable upon a valve seat within a valve body and controls flow between inlet and outlet openings on opposite sides of the valve seat. An actuator such as a solenoid actuated armature is provided to controllably drive the valve axially and open the valve in a controlled manner to obtain the amount of EGR required under various engine operating conditions. A valve spring biases the valve in a closing direction to close the valve when the armature is returned to the initial valve closed position.
Where a large variation in EGR flow is required, the pintle head and orifice are shaped to provide the required variation in flow. However, a relatively long travel of the armature may be required in such valves. In addition, the solenoid force required to open the valve from the closed position must be large enough to overcome unbalanced pressures in the valve body or seat tube so that a relatively large solenoid coil and armature maybe needed. It is accordingly desired to provide a solenoid or otherwise actuated EGR valve that operates with a lower actuating force while providing a full range of controlled exhaust gas recirculation flow.
The presentation invention provides two stage exhaust gas recirculation (EGR) valves that can deliver a wide range of EGR flow while operating with reduced valve actuating forces. A reduced cost actuator, such as a solenoid actuator with smaller sized coil and armature, may thus be used for actuating the valves. An attached valve body mounts dual pintle valves including a larger first valve which engages a valve seat in the valve body to control exhaust gas flow between inlet and outlet openings on axially opposite sides of the valve seat. A smaller second valve is positioned inside the first valve and engages a second valve seat in the head of the first valve. The second valve controls a low flow passage inside the first valve to also control a lower volume of exhaust gas flow between the inlet and outlet openings.
The solenoid armature engages only the smaller second valve during a first stage of its stroke so that the smaller valve is opened first and flow control is maintained in a low flow range. Exhaust and intake pressures acting on the second valve require low force to overcome because of the smaller area of the second valve. In a second stage of its stroke, the armature also engages the first valve, forcing it off its seat and providing a greater amount of exhaust flow. Opening of the larger first valve requires less force than single pintle valves because the flow from the open smaller valve reduces the opposing opening of the larger valve.
The dual concentric pintle valve design may also be applied to partially or fully balanced valves to provide better control of EGR flow over the full control range of the valve. Additional effective travel of the valve armature may be obtained by underlap of the armature and its magnetic pole so that the smaller valve is opened as the armature force increases to a maximum, leaving the maximum armature force for opening of the larger valve.
These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings.